Most animals that don't live as long as we do are
also smaller than we are. A lot of things are
proportional to how big an animal is, and
scientists think it has something to do with how
our bodies use oxygen to 'burn' the food we eat.
I think bigger animals, such as elephants, live
longer than we do. Scientists are still trying to
understand all this. Pigeons and rats are the
same weight, but rats live about 4 yrs and pigeons
live about 40 yrs! Scientists have found that
rats produce toxic chemicals ("radicals") from
oxygen 10 times faster than pigeons do, so they
think this is why rats die off faster. Also,
scientists found that animal cells all live about
the same length of time when they're grown in
petri dishes in the lab, whether they come from a
big animal with a long lifespan or a little animal
with a short lifespan. It's a complicated question.
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